Communications: radio wave antennas – Antennas – With vehicle
Reexamination Certificate
2000-05-23
2002-03-12
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
With vehicle
C343S873000
Reexamination Certificate
active
06356236
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transparent sheet, particularly glazing provided with a coating and with a radiation window.
2. Discussion of the Background
These features are known from document DE 19 503 892 C1 which describes measures for reducing the screen effects of coated panes with respect to information-carrying microwave radiation. Glazing of this type, coated with electrically conductive and optically transparent layers, find application as thermally insulating glass, which reflects infrared radiation, and/or as glass that can be electrically heated and intended for use as glazing in buildings and vehicles.
In the case of vehicles, such glazing forms, together with a metal body, a Faraday cage which projects the interior of the vehicle against electromagnetic fields. In a building, it is also possible to protect rooms electrically by using panes provided with an electrically conductive coating and a conductive configuration on the other wail parts. Protective enclosures of this type can protect sensitive equipment, such as central computers, against disruption caused by powerful radio transmitters or by radars.
On the other hand, the protective enclosure does not let any microwave-type electromagnetic radiation pass through it, such radiation being used as a carrier wave for information. When a transmitter and/or receiver provided with an antenna is in a protected passenger compartment (vehicle), transmission problems arise. For example, vehicle position indication systems, remote control systems, identification systems and systems for recording payment charges may be subject to disruptions.
In a known manner, the layer systems may be post-structured by removing, in a linear manner, the layer previously deposited continuously, and to do so by mechanical or thermal means. In particular, exceptionally narrow slots may be made in the layer by means of laser beams. According to the aforementioned prior art, the electrically conductive layer is provided with at least one slot acting as a radiating slot, with a very short length and a very small open area, this length and open area being matched to the wavelength of the microwave radiation, via which slot the radiation energy absorbed by the conductive layer has to be re-emitted in the microwave range in the form of radiation energy. When the effective frequency for data transmission rises, for example to 5.8 GHz, as is intended for the automatic recording of payment charges on motorways, and when the slots are essentially provided for transmitting microwaves at this frequency, they are advantageously dimensioned so as so have a resonant length of &lgr;/2, taking into account the dielectric constant of the glass. For the frequency mentioned, which corresponds to a wavelength &lgr;=52 mm, the length L of the slots is 18 mm. Their width does not play a primary role and is, for example, 0.1 mm. The mutual separation of the slots, both in the horizontal direction and in the vertical direction, is indicated depending on the resonance and is 18 mm.
If the data is transmitted by means of circularly-polarized microwaves (i.e. the plane of instantaneous oscillation of the waves rotates about its direction of propagation in such a way that the waves oscillate within an envelope of circular form), cruciform recesses are advantageously provided in the layer. The length of the two slots is again advantageously matched to the wavelength of the microwaves used and corresponds to the value &lgr;/2 of the waves used, caking into account the dielectric constant of the glass.
Comparative measurements relating to the attenuation of microwave radiation at a frequency of 5.8 GHz demonstrate, in the case of this prior art, that glazing made of laminated glass having radiating slots in the coating makes it possible to achieve a markedly lower attenuation of the transmission for high-frequency radiation than glazing made of coated laminated glass, and an attenuation approximately equal to that of glazing made of uncoated laminated glass is possible.
In the case of many applications, particularly in motor vehicles, it is essential to obtain, only within a relatively small limited window region, as high a radiation transmission or as low an attenuation as possible. The antenna of the on-board unit (transmitter and/or receiver) of the transmission system must be linked to this window region. The distance separating the antenna from the internal face of the glazing is predefined by the system and is, for example, equal to half the wavelength of the useful information-carrying radiation, that is to say about a few centimeters. According to the state of the art, it is not, however, always possible with individual slots in the layer uniformly distributed over the glazing face, to achieve the strong local transmission required for the systems of this type in the direct coverage region of the antenna of the on-board unit.
Glazing covered with a transparent layer, in which a checkerboard pattern is produced using a laser, is already known from document DE-A-195 41 743. This network, which extends over the entire glazing, is designed to reduce the screen effect of the glazing, provided with a layer, with respect to electromagnetic radiation. The distance separating the lines of the pattern from each other must, according to this document, be less than 2.5 cm and thus less than half the wavelength of the microwaves which are supposed to pass through the glazing. However, this document makes no reference to the ratio between the uncoated area and the coated area.
It is also known, from document DE 4 433 051 C2, how to produce a radiation window while keeping a continuous and limited area of glazing without any layer. For example, a mask is laid on the glass, or on the film, during application of the coating, or the layer material is again removed after it has been applied. Apart from the relatively high cost, somewhat undesirable side effects may appear in these constructions, such as a coloration subjectively perceived by an observer in the uncoated region. For the purpose of avoiding these effects, the surface part in question may be made opaque using a colour layer applied, for example, by screen printing. In the case of glazing made of laminated glass, the colour layer must be on the internal side of the external pane, again in front of the functional layer. This arrangement of the colour layer presents considerable disadvantages for the manufacturing technology, particularly during the process of bending the glazing. The glazing purchaser is not always willing to accept the reduction in transparent area which using glazing with a window entails.
SUMMARY OF THE INVENTION
The object of the invention is to provide glazing with a radiation window in a coating which, while being barely visible optically and able to be generally applied in the case of various system configurations, ensures good transmission of high-frequency radiation, at least in a region of limited area, without reducing the attenuation or Reflection function of the coating in the other regions.
Tests on glazing with functional layers, particularly on glazing made of laminated glass, in which a coated film is incorporated, have demonstrated that the transmission of microwaves through structured coatings (whether on glass or on a film) depends above all on the area permeable to radiation, that is to say the area free of the layer material or stripped of this material. Taking a unit area as reference, the optimum transmission value must be determined by varying the ratio of, on the one hand, the area actually permeable to radiation, or uncoated area, to, on the other hand, the total unit area.
The given total unit area is, for example, 100 mm
2
, of which in total 25 mm
2
are devoid of coating. The abovementioned ratio is therefore a quarter (25%). In regions where the layer is continuous, the quotient is therefore 0 and, in known windows free of coating over their entire surface, it is 1. Tests have confirmed that it is only wh
Immerschitt Stefan
Maeuser Helmut
Le Hoang-anh
Saint-Gobain Glass France
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